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Sowing and Starting off Tomatoes – Introduction to Tomato Growing Part 2

This article covers the life of your tomatoes from sowing the seeds to transplanting the seedlings into pots ready to plant out in their final positions.

Tomatoes Potted On

Tomatoes growing away strongly in pots.

Sowing the seed

I start off all my tomatoes in the same way between late February and early March by sowing thinly into a standard multi-purpose potting compost in small 2½” pots, lightly covered with compost or vermiculite and placed in a heated propagator at 20ºC. A warm windowsill will also suffice.

My experience has been that starting tomatoes off too early is counter-productive. The day length is too short and the light intensity too low to get strong seedlings. Consequently the seedlings become ‘drawn’ – long, thin spindly shoots trying to get out of the shade into the sunlight, which is just not there. Although you can rescue these by planting deeply, later sown seeds seem to catch up and even overtake the earlier.

Also, when moved into the greenhouse, it is harder to maintain a reasonable temperature – unless you can afford a heated greenhouse. Even in mid-March you need to watch out for really cold nights. In Britain we hardly have climate but we do have weather!

To defend against cold nights I place horticultural fleece over the seedlings, using some short sticks to keep the fleece from pressing down on the seedlings.

Potting On the Tomato Seedlings

When these have germinated and are about an inch high, I move them into individual modules in a seed tray, which are grown on in the greenhouse. Research has shown that they do best if transplanted within 6 days of germination. Pots indoors will do if you do not have a greenhouse.

When they outgrow the modules, I select the best and move them on to 3″ pots. I always ‘plant deep’, about half way up the stem at each stage. This encourages root formation, which the plant will need to supply the demands I am going to make upon it.

You could probably cut out the module stage – but I always expect to lose a few seedlings on transplanting so this gives me ‘spares’. Moving from modules to pots does not place any strain on the plant so I do not plan on losses at this stage.

Some particularly vigorous varieties may need to move to an even larger pot before they reach their final position.

You can, of course, buy tomato plants from nurseries but generally I prefer to grow my own from seed as you the range of varieties to buy as plants may be limited.

Moving the tomato seedlings on – how to pot on tomatoes

Tomato Seedlings

In this picture you can see the seedlings in the small pot – they are drawn (pulled long) from the low light level in the house. There are about 20 seedlings in the small pot
The module insert is filled with an ordinary multi-purpose compost.

Having removed the seedlings from the pot, dib a hole into the compost and drop the seedling in. Select the best of the seedlings with roots undamaged. Handle very gently by the leaves to avoid damage to the stems. By planting deep the plant is encouraged to form more roots from above the old root line.

Having removed the seedlings from the pot, dib a hole into the compost and drop the seedling in. Select the best of the seedlings with roots undamaged. Handle very gently by the leaves to avoid damage to the stems.
By planting deep the plant is encouraged to form more roots from above the old root line.

Tomato Seedlings Potted Up

Six healthy tomato seedlings ready to grow on Just like nature, we select for the best. Starting with seeds, then selecting the best seedlings and finally planting the best three of six plants.
Usually these would go out into the deep propagator in the greenhouse

In very cold weather or lack of warm green house, the modules with the tomato seedlings are brought on in the window sill.

Unfortunately they do get drawn by the lower light level. Fixing some kitchen foil to cardboard and standing this behind the modules will help by reflecting more of the light on to them

This is the point where my treatment of the tomato seedlings changes according to whether I am intending to grow them as outdoor tomatoes or under glass.

Further Information: Tomato Growing Guides